1. Field of the Invention
The present invention relates to an organic light emitting diode (“OLED”) device in which a lower layer structure is modified to improve light transmittance and a method for manufacturing the same.
2. Description of the Related Art
Of flat panel display devices, an OLED device is an emissive display device and attracts public attention as a next generation flat panel display device due to merits of a fast response speed, the compact thickness, low manufacturing cost, and a high contrast.
A typical OLED device comprises an anode arranged on a substrate, a light emitting layer (“EML”) arranged on the anode, and a cathode arranged on the light emitting layer. When a voltage is applied to the anode and the cathode, holes and electrons are injected into the light emitting layer, holes and electrons are recombined in the light emitting layer, generating exitons. The OLED device emits light by energy generated when the exitons transitions to a ground state from an excited state.
The OLED device is divided into a bottom emission type and a top emission type according to a direction in which light generated from the light emitting layer is emitted. In the bottom emission type, light is emitted in a down direction of a substrate, and a reflective electrode is formed on the light emitting layer and a transparent electrode is formed below the light emitting layer.
The OLED device comprises a red (“R”) light emitting layer, a green (“G”) light emitting layer, and a blue (“B”) light emitting layer in order to realize a full color. In this instance, the light emitting layers of respective colors have different lifespans. For this reason, it is difficult to maintain a white balance if it is driven for a long time. In order to resolve the above problem, a light emitting layer which emits a single color is formed, and a color filter is formed to extract light of corresponding colors from light emitted from the light emitting layer.
An OLED device recently developed has a color filter on array (“COA”) structure in which a color filter for converting a color of light below the light emitting layer is arranged on a single substrate. In this instance, if a transparent electrode is formed above the color filter, a surface becomes non-uniform due to dyes or pigments of the color filter, so that an electric field applied to the light emitting layer becomes irregular. An overcoat layer is formed on the color filter to prevent a non-uniform surface and maintain a constant electric field in the light emitting layer. Here, a silicon nitride layer which is used in a thin film transistor (“TFT”) is formed below the color filter. In the OLED device with the COA structure, due to the thickness of the overcoat layer and the silicon nitride layer, transmittance of light emitted from the light emitting layer changes, thereby deteriorating brightness and a color gamut.